Dear Arman,
Thanks a lot for using Behance Portfolio Manager.
Regarding the API calls, you can increase it by requesting a premium access to Behance by contacting them from here:
https://behancenetwork.zendesk.com/anonymous_requests/new
The reason for not saving the completed project is, the user of the project wight change the project afterwards, thus making the Project stored in website outdated. Plus it saves the disc space, since normally the limit does not exceeds 150.
However, if you wish to store the complete project, we can do that as a custom development service just for you. Please let me know if you wish to do this and I'll send you an estimate.
Last but not the least, please don't forget to rate us on JED:
http://extensions.joomla.org/extensions/directory-a-documentation/portfolio/27668